Adding pieces of one size

Cut a strip into 8 equal parts. Slide 3 parts together. Put 2 more parts next to them. Now there are 5 parts, all the same size.

The rule

Parts of one size are easy to add. The tops add. The bottom number does not change.

The parts are the same size. So the bottom does not change.

Subtracting works the same way. The tops subtract. The bottom stays.

Example

Add the tops: 3 + 2 = 5. Keep the bottom 8. So 3/8 + 2/8 = 5/8.

Subtract the tops: 5 − 3 = 2. So 5/8 − 3/8 = 2/8.

4/8 + 4/8 = 8/8, because 4 + 4 = 8. All 8 parts make one whole.

Parts of different sizes need renaming first. 1/2 = 2/4. Then 2/4 + 1/4 = 3/4.

In the lab, drag loose pieces onto the strip to add. Drag pieces off to subtract.

Try the lab to finish this lesson.